The use of Radio Frequency (RF) power transistor devices as signal amplifiers in wireless communication applications, and in computing systems in general, is well known. In recent years, the operating frequencies for such devices have increased dramatically and are now well into the gigahertz range. As the frequencies continue to increase, the specific design characteristics of the transistor devices become increasingly important.
A typical RF power amplifier includes a package, or package substrate, with one or more microelectronic dies, each having multiple transistors formed thereon, mounted on the package substrate, along with one or more shunt caps to modify the overall impedance of the power amplifier. Input and output leads are also connected to the package substrate, and wire bonds are typically used to make electrical connections between the various components.
As a RF signal passes through the RF power amplifier, different portions of the current associated with the signal travel different path lengths. For example, due to the “skin effect,” as current leaves the RF power amplifier through the output lead, a majority of the current will be located near the outer edges of the lead. As a result, the current passes through the RF power amplifier unevenly. Additionally, an increased amount of current tends to flow through the ends of the transistor dies. This uneven current flow leads to some of the wire bonds overheating and being damaged.
Furthermore, different portions of the current flowing through the RF power amplifier will experience different impedances. These impedance mismatches hinder the performance of the amplifier.
Accordingly, it is desirable to provide a RF power amplifier with the capability to handle varying amounts of current across different portions thereof. In addition, it is desirable to provide a RF power amplifier with a specifically controlled (e.g., more constant) impedance across the different portions thereof. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.